1. Field
The present invention relates generally to removing materials from liquids, and more particularly to adjacent opposed, oppositely moving blades for, and methods of, moving sludge in a sludge collection basin for removal of the sludge from the basin.
2. Description of the Related Art
In the past, containers (e.g., basins or tanks) have been provided to house apparatus in which materials are collected. The materials may have any of a wide variety of compositions, and generally consist of pieces of the materials that move under the force of gravity to the bottom (or floor) of the basin (“settleable-particles”). For example, in municipal waste water systems, the materials may be formerly biologically-active waste materials that are no longer biologically-active, and that are in the form of the settleable-particles.
For ease of description, materials within the wide range of compositions and that consist of the settleable-particles, are referred to as “particles”, and in the context of particles that have settled, or moved, to the bottom of the basin, such materials are referred to as “sludge”.
The settleable-particles may be collected from liquids by plate or tube settlers that promote settling of the settleable-particles to the bottom of the basin. In other cases, flocculators may be housed in such containers. Settleable-particles often inadvertently move in the flocculators to the bottom of the basin. Because the flocculators are designed to circulate liquid and materials, rather than to promote settling of the materials, the materials that inadvertently collect at the bottom of the basin present a problem.
In the case of the settlers, for example, the sludge must be removed from the bottom to make room for more sludge collected from more liquid and materials that flow into the basin. In the past, sludge removal equipment has been mounted on or near the bottom for moving the sludge along the bottom to sludge outlets that allow removal of the sludge from the basin. The moving has been done by scrapers that are mounted together for traverse together from one end of the basin to an opposite end of the basin. On each traverse in one direction, each of the scrapers pushes sludge in the same direction to the outlet at one end. On each reverse traverse in the opposite direction, each of the scrapers pushes sludge to the outlet at the other end. In this scraper system, the scrapers must be able to push the sludge in each of the directions, and move together in the respective direction to perform the pushing.
Others have attempted to use scrapers of a different design, in which the scrapers need only be able to push the sludge in one direction across the bottom while moving together in the one direction to perform the pushing. In the use of these different scrapers, such as those described in U.S. Pat. No. 5,431,818 to K. D. Zickert issued Jul. 11, 1995, the distance through which each of the scrapers is moved has been greatly reduced, e.g., to about two feet. Problems are described in that patent in the use of a wedge-shaped scraper having a generally right-triangular cross-section, such as the scrapers 30 shown in FIGS. 1A and 1B. Many such scrapers 30 are attached to one net 32. The one net 32 is moved in a “to” (forward, sludge-moving direction, arrow 34) and in a “fro” (return, or reverse direction, arrow 36) reversing traverse. In this manner, the one net 32 moves all of the scrapers 30 together in one time period (TP) through the two foot distance in one direction (e.g., the forward, “to”, direction 34, FIG. 1A). The one net 32 then reverses, and moves all of the scrapers 30 together in a next TP through the same two foot distance in the opposite direction (arrows 36, FIG. 1B).
In an effort to increase the efficiency of sludge movement in the forward direction 34, in U.S. Pat. No. 5,431,818 the cross-section of the scrapers 30 was modified, and all of the modified scrapers 40 (FIGS. 1C and 1D) were moved together in the same “to” direction 34 and together in the “fro” direction 36 at controlled speeds in the same time periods. Unfortunately, that cross-section of the modified scrapers 40 was made more complex by the selection of a curved configuration 41 shown in FIGS. 1C and 1D. That configuration 41 was described as a downwardly facing bottom surface 42, a substantially oblique, convex surface 44, and a substantially vertical, concave surface 46 facing in the forward direction (arrow 34). The complex, modified scraper 40 was said to minimize turbulence.
However, Applicant's analysis of the complex modified scraper 40 indicates that those advantages may be offset (i.e., substantially reduced) by many factors. One such factor is the movement of all of the scrapers 40 together (i.e., in the same direction at the same time). Applicant's analysis indicates that there is a tendency, for example, for undesired movement of the sludge in the return direction 36 due to all of the scrapers 40 moving together (at the same time in the return direction 36), which tendency is also promoted by the one net 32 attached to and moving with all of the blades. The undesired movement in the return direction reduces the efficiency of the desired movement in the “to” (or forward) direction.
Also, although the one net 32 is described in U.S. Pat. No. 5,431,818 as being pulled in the forward direction 34, and as being pulled in the return direction 36 (as by a spring), there are commercial embodiments that appear similar to the above-described system that uses the complex modified scrapers 40. Those commercial embodiments have the one net 32 reinforced and driven by a structural drive member (not shown) that has high resistance to both tension and compressive forces exerted parallel to the directions 34 and 36. Thus, in commercial practice, an extra structural member has been used to apply respective “to” and “fro” forces to the one net 42 to cause the to and fro motion. Such an extra structural member has increased the cost and weight of those commercial embodiments, and the extra weight increases the required energy (e.g., electrical power and thus operating cost) to move the scrapers.
Applicant's analysis further indicates another disadvantage of the substantially oblique, convex surface 44 (or the right-triangular cross-section of the blades 30), in combination with all of the modified scrapers 40 (or all of the scrapers 30) moved together in the same “to” direction 34 and together in the “fro” direction 36 in the same time periods. As noted, this structure and movement results in undesired movement of the sludge in the return direction 36 due to all of the scrapers moving together (at the same time in the return direction 36). In an apparent attempt to reduce the undesired movement of the sludge in the return direction 36, the U.S. Pat. No. 5,431,818 teaches use of a higher speed for the return stroke than for the forward stroke (e.g., 12 m/minute return vs., 3 m/minute forward). Such a higher speed return stroke can agitate the particles of the sludge causing some of the particles to be reintroduced into the liquid that was clarified by the settler, for example. This further reduces the efficiency of the overall operations because the reintroduced particles have to be again settled and then removed from the basin.
Applicant's analysis further indicates yet another disadvantage of all of the scrapers 30 or 40 moving together in the same “to” direction 34 and together in the same “fro” direction 36 in the same time respective periods. All of the prior push surfaces (e.g., 46) engage and push the sludge at the same time and are thus resisted by the sludge at the same time. The requirement for higher power for this pushing of all blades together at the same time, and the increased weight of the extra compressive member that enables pushing instead of pulling the structure, result in the motor used for moving the system being more costly than a lower-power motor. Also, such extra compressive member makes the net 32 less compliant with respect to uneven floors of the basin, which in turn results in higher costs to initially provide a smoother floor for the basin (e.g., of concrete) and higher repair costs in not damaging the smoother floor of the basin during repair.
Lastly, if a generally-triangular cross-section blade is to be used, there is additional cost to manufacture the convex and concave shapes of the scrapers 40.
Accordingly, there is a need for a sludge system and methods that reduce the tendency of the sludge to be moved in the return direction 36 (such tendency being caused by all of the scrapers moving together in the same return direction during a given time period). Further, there is a need for such system and methods to avoid the need, in actual commercial practice, for the use of any structural drive member other than the one net (or a main frame) that supports (or carries) the blades themselves. Thus, there is a need in actual commercial embodiments to eliminate the above-described extra structural drive member that has high resistance to both tension and compressive forces exerted parallel to the directions 34 and 36. Also, there is a need in actual commercial embodiments for the individual scrapers, or blades, to have a configuration manufacturable in a low-cost manner.